Quality
Waterjet Newsletter – 04/22/2007
Optimal
Standoff Distance in Waterjet Cleaning Last year Gu
et al.* presented a paper on the subject of optimal standoff distance in high
pressure waterjet cleaning. Here are the
highlights. Experimental data of jet striking
force with water jets of 0.97 to 3.57 mm in diameter striking at the target
perpendicularly were shown in the plot below. This plot indicates that the
strike force of the jet reaches its maximum when the ratio of standoff
distance L and nozzle diameter D0 is 100. Calculations were done
to offer explanations for this phenomenon.
The strike force of a continuous
water jet can be calculated with this equation:
where rw
is water density, Q flow rate, and v speed of jet. However, as the standoff
increases, air will be mixed into the jet to turn it into a spray. The
density of the air/water mixture rm was
related to the standoff distance and nozzle diameter with this equation:
When the air content, expressed
with the ratio a= (rw-rm)/rm, exceeds 1/10 – 1/6, the water spray will
transform into an air bubble spray. The strike pressure of the air bubble
spray pi can be calculated with Lord Rayleigh equation:
where ps
is the strike pressure of a normal water spray The strike pressure of an air
bubble spray is typically 8.6-12.4 times of a normal water spray. When the
L/D0 ratio is 100, the air content is 52% and thus an air bubble
spray is formed. Even though the density of the air/water mixture is
decreasing as the standoff distance increases, the combination of air bubble
bursting and spray striking actually enhances the strike pressure. But when
the L/D0 ratio is more than 100, the strike force attenuates. * Gu, Chun, Li, Angui, & Liu,
Tingcheng (2006) Optimal standoff distance of water
spray cleaning, in Proceedings of the 8th Pacific Rim
International Conference on Water Jet Technology, Oct. 10-12, Qingdao, China,
Paper 31. |
|
QualJet LLC
Quality Waterjet Spare Parts Specialist · Quality
Waterjet Spare Parts o Meets/exceeds
OEM standards o 30%
longer operation life time than competing products · Extensive
Parts Coverage for: o Flow
style, IR Style o 40K/55K
pumps o Intensifiers
o On/off
valves o Cutting
head o Swivels · OEM
Expert o 20+
year waterjet OEM experience (via OH Precision) o Accept
small OEM order Durable, Compact 40K
PSI Pumps
· Long
operation lifetime · Highly
cost-effective · Light
weight and compact · Contact
us for o
Custom power end o
50K psi models o
Private labeling o
Custom design QualJet LLC
1-866-QUALJET (782-5538) Fax: 425-378-7776 Email: info@qualjet.com Website: www.qualjet.com To unsubscribe the
newsletter: unsubscribe@qualjet.com For newsletter archive: www.qualjet.com/Newsletter.htm
Copyright ©2005, QualJet LLC |
|
|
